Another customer tweeted: "@TSB left me unable to pay for my shopping and no access to my money. TSB are a joke."

Another Twitter user wrote: "This problem is also affecting Halifax debit cards as I found out trying to pay for lunch with my wife!"

TSB chief executive Paul Pester said in a tweet as the difficulties were being experienced: "My apologies to TSB customers having problems with their cards. I'm working hard with my team now to try to fix the problems."

A Lloyds Banking Group spokeswoman said at that time: " We are aware that some customers are unable to use their debit cards either to make purchases or to withdraw money from ATMs. We are working hard to resolve this as swiftly as possible and apologise for any inconvenience caused."

A TSB spokeswoman said: "We are aware that some TSB customers are unable to use their debit cards either to make purchases or to withdraw money from ATMs. This has impacted all Lloyds Banking Group brands. We are working hard to resolve this and unreservedly apologise for any inconvenience caused."

A Lloyds Banking Group spokeswoman said later that the problems had been resolved.

She said: "We apologise that earlier today, between 3pm and 6pm, some customers were unable to complete their debit card transactions. Although the majority of transactions were unaffected, we are very sorry for the inconvenience that this will have caused.

"At the same time, some customers encountered problems at approximately half of our 7,000 ATMs. This was resolved by 7.30pm, and all of our ATMs are now working."

Online and telephone banking were unaffected by these issues, and c ustomers were still able to withdraw cash from other ATMs.

The spokeswoman was unable to say how many people were affected.

Mr Pester said later: "I am pleased to confirm that the problems causing some debit card and ATM transactions to fail earlier today are now fixed. I apologise once again to all our customers who were affected.

"Some customers may still experience a short delay making payments this evening as we are currently working through the backlog of payments from this afternoon. But rest assured we are working as quickly as possible to restore a normal service."